Bus saturation is deemed as one of the primary causes of delays in the data propagation between spacecraft components. However, the conditions under which bus congestion can affect measurements variability were not well characterized before. This paper presents a bus saturation model and a set of experiments to characterize the bus performance of satellite missions for different traffic load, data rate, and synchronization periods. The results showed an increase of measurements variance of up to 18% caused by bus saturation. Additionally, an algorithm was proposed to reduce the data delay by controlling the saturation on the communication channel at the operational level.

Spacecraft buses using distributed software architectures have been adopted in space missions design due to their increased performance and reliability. However, to achieve reliability in highly distributed systems, fault-tolerant mechanisms must be implemented to mitigate the anomalous behavior of components and software processes. One of the most significant challenges in designing distributed software is related to the consensus of processes running in parallel. For instance, consider the attitude determination and control subsystem is trying to estimate the current satellite's attitude state. For that purpose, it must request measurements to multiple sensors connected to the spacecraft data bus, and it needs to organize this information in the right chronological order for proper state estimation. A wrong data sequence can lead to an increased pointing error during satellite operations. Consensus protocols in distributed software architectures are mainly focused on voting mechanisms, which work well when the process in charge of the decision making (leader) does not fail. In an execution environment with faulty processes, the system can reach decisions that do not reflect the actual status of the system due to corrupted or missing information. This paper describes and analyzes software consensus scenarios in spacecraft with synchronous and asynchronous data buses. These scenarios include state estimation with networked components and, temporal consistency of telemetry packets. The work presents a comparison of performance characteristics for different consensus strategies. It takes as a reference the Paxos algorithm family to establish an optimal configuration for achieving consensus in distributed software architectures for satellite systems. The proposed approach presents an agent-based implementation of the Paxos Algorithm to reach a consensus under intermittent failures, as well as analyzing scalability issues. Finally, the work proposes the adoption of software design patterns that guarantee consensus on time-critical processes such as attitude determination and control. The results enable to define and evaluate software performance and reliability concerning the criticality of its processes to achieve consensus. It also facilitates fault detection and recovery capabilities by design, during the software development phase of the satellite. Finally, a set of software design rules is provided that can be used to improve the resilience of satellite's onboard software.

Costa Rica is world-renowned for its environmental conservation and its clean energy generation. The government-led programs such as the Environmental Services Payment Program has resulted in an increase of the country's forest coverage from 21% in 1987 to 51.4% in 2010. Additionally, the country has established an ambitious goal of becoming a carbon neutral entity by 2021. Many efforts have been developed to contribute to this objective, including Irazu, a project consisting of designing, manufacturing, launching and operating the first Central American satellite to monitor carbon fixation in an experimental forest plantation in Costa Rica. The Irazu project is an initiative of the Central American Association for Aeronautics and Space (ACAE) and the Costa Rica Institute of Technology (TEC), along with many contributors from academia, government, and the private sector. Irazu uses a 1U CubeSat that will act as a Store and Forward system, to collect data from ground sensors in a remote location and forward them to a data analysis and visualization center in TEC. The ground sensors measure tree diameter growth, soil humidity, and meteorological parameters. The data collected is used to estimate the amount of carbon that the trees are absorbing and to observe how this is affected by meteorological variables. Furthermore, this data, along with the spacecraft operating parameters, will be published in a user-friendly website to promote science and technology for Costa Rica's future generations. This paper focuses on the final testing of the spacecraft, which is critical for launch certification, and mission operations. The final testing was performed at the Laboratory of Spacecraft Environment Interaction Engineering of the Kyushu Institute of Technology. Strict requirements set by the launch provider had to be met, which is why this phase included vibration testing, thermal vacuum testing and fit tests of the CubeSat in the JEM Small Satellite Orbital Deployer, among others. Furthermore, the process of obtaining the operating frequency and license of the satellite for a first-time applicant nation is explained. An overview of the operations is presented as well, including a summary of the ground sensor network and how they establish the communication link with the CubeSat, how the satellite stores the data, and how it forwards it to the research center at TEC.

In 2007, the Government of Costa Rica announced to the world its ambitious goal of turning into the first carbon neutral country by 2021. Following the announcement, governmental institutions, universities, NGOs and private companies have worked arduously on the creation of different initiatives to reach that goal. One innovative project is Irazú, consisting of the design, construction, launch, and operation of the first Central American satellite. The project is not just intended to enable a baseline for training scientists, engineers, and managers in the necessary skills to execute an end-to-end space project. It also aims to demonstrate a CubeSat Store & Forward (CS&F) System that enables transmission of biomass and carbon dioxide fixation data from a remote fast growth tree plantation in the lowlands of Costa Rica to a research facility for its post-processing and analysis. The Irazú project is led jointly by the Central American Association for Aeronautics and Space (ACAE) and the Costa Rica Institute of Technology (TEC). It also involves a variety of national and international stakeholders from government, academia, and industry. This paper is a continuation of previous reports on Irazú that were presented at the Workshop on Small Satellite Programs at the Service of Developing Countries over the last five International Astronautical Congresses. The project has already reached major milestones, such as the approval of the final design presented in the Critical Design Review (CDR), successful assembly of the manufactured structure and the components received from different CubeSat component providers, and successful performance during various environmental tests. The mission and satellite system architecture for a CS&F system were defined, which included the three primary components: the remote station, the spacecraft, and the ground segment. Experts from the National Aeronautics and Space Administration (NASA), Kyushu Institute of Technology (Kyutech) and Delft University of Technology (TU Delft) revised the design of Irazú. Advances in the Assembly, Integration & Testing (AI&T) phase are presented and discussed, which include the development of spacecraft components, testing of the communication link, assembly of the satellite and initial results of environmental testing. International cooperation is emphasized in this phase, because Costa Rican engineers carry out testing at the laboratories of the Kyushu Institute of Technology. Furthermore, advances in the satellite frequency coordination process and spacecraft registration for an emerging space nation are presented, as well as the lessons learned from the AI&T phase.

In the last two decades, CubeSats have changed the perception of satellite missions aided by standardization and usage of commercial-off-the-shelf components. CubeSats have also proven the feasibility of low cost and short development time space missions. The PocketQube with a form factor of 5x5x5 cm has been proposed as the next class of spacecraft to benefit from miniaturization. This paper presents a comparison between the two standards and analyzes the impact of miniaturization on spacecraft design and performance. At satellite level, the reduction of volume has a tremendous impact on the available power and makes energy management and efficiency critical. Thermal issues become important due to the reduced thermal capacitance, leading to higher thermal swings and larger temperature variations than CubeSats. The other important impact on the satellite bus is the reduced communication capacity due to several reasons: the reduced volume limits the available antenna size and also the available power available. At mission level, other factors have a substantial impact: de-orbit time becomes a major criterion in the launch selection process to comply with orbital debris policy. The volume reduction also affects the radar cross-section making the satellite more difficult to detected for space surveillance radars. Despite these challenges, PocketQubes are an attractive standard currently for academic and research groups as a way to reduce the cost and development time considerably. Payload capabilities also can force a paradigm shift from single to multiple satellites more than it was already happening with CubeSats: PocketQubes could better fit certain niches where high spatial or temporal resolutions are required instead of full resolution. Distributed space weather monitoring could be an interesting application where specific phenomena could benefit from multi-point sensing. All these strong points can also be coupled with a bigger satellite to complement and enhance its capabilities. Delfi-PQ is a PocketQube currently being developed at TU Delft using an agile approach, contrary to the typical V-model design. Shorter life cycle development benefits students, allowing them to get more involved in every iteration. The reduction in cost and development cycle increases the launch frequency. Incremental engineering becomes fundamental, also providing benefits on the reliability side because flight experience becomes more frequent than when following traditional development strategies. End-to-end development motivates students and provides them with a better insight into real-world engineering opportunities and training experiences. With this strategy, technical and educational objectives are more aligned, and the integration of such a project in the curriculum is facilitated.